Ab initio molecular-dynamics study of liquid GeSe2

The structural, vibrational, and electronic properties of liquid GeSe2 are investigated using ab initio molecular dynamics. The static structure factor S(Q) and the pair-correlation functions of our model are in good agreement with experiment. We find many similarities between the topology of the liquid and the glass state. In addition we introduce a way of characterizing the intermediate-range order of liquid and glassy GeSe2 through fourfold and sixfold rings. The overall vibrational density of states is found to be consistent with Raman experiments. The intensity of the low-frequency modes, splitting of the A, and A,, peaks, and the decrease in the intensity of the high-frequency modes are all reproduced. The electronic density of states is determined and compared to our results for glassy GeSe2. We find that an increase in Se bond length and bond-angle disorder significantly broadens the conduction band. The time-dependent behavior of the electronic eigenvalues is examined and transient events are observed in which an electronic state crosses the optical gap. The structural configurations which produce states in the optical gap are determined using an ab initio molecular-dynamics approach and are found to be in agreement with experimental photoluminescence and electron-spin-resonance data. We also find that a linear relationship exists between the root mean square of the thermal fluctuations of an electronic eigenvalue in time and its localization.